This paper investigates the nano-macro transition in magnetic shape memory alloy(MSMA) thin films using a recently developed sharp phase front-based three-dimensional (3D) constitutive model outlined by Stoilov (JSMS 2007), and originally proposed in the 1D context by Stoilov and Bhattacharyya (Acta Mat 2002). The key ingredient in the model is the recognition of martensitic variants as separate phases in a MSMA domain. Evolution of the interface between these phases is taken as an indicator of the process of reorientation in progress. A formulation of the Helmholtz free energy potential based on Ising model has been derived. The implications of the external magnetic field on the initiation of phase transformation are studied for various mechanical loading modes.

This paper investigates the nano-macro transition in magnetic shape memory alloy(MSMA) thin films using a recently developed sharp phase front-based three-dimensional (3D) constitutive model outlined by Stoilov (JSMS 2005), and originally proposed in the 1D context by Stoilov and Bhattacharyya (Acta Mat 2002). The key ingredient in the model is the recognition of martensitic variants as separate phases in a MSMA domain. Evolution of the interface between these phases is taken as an indicator of the process of reorientation in progress. A formulation of the Helmholtz free energy potential based on Ising model has been derived. The implications of the external magnetic field on the initiation of phase transformation are studied for various mechanical loading modes.

Important advances in multi-scale computer simulation techniques for computational materials science have been made in the last decade as scientists and engineers strive to imbue continuum-based models with more-realistic details at quantum and atomistic scales. One major class of multi-scale models directly couples the atomistic detail to the macro region modeled using continuum concepts and finite element methods. Here, the development of such coupled atomistic/continuum model is presented within a single coherent framework with the aim of providing quantitative description of the constitutive behavior of magnetic shape memory alloys. A formulation of the Helmholtz free energy potential based on one-dimensional Ising model has been derived. The developed thermodynamic potential has been used in the context of the sharp phase front-based continuum model of the first order phase transformations suggested by Stoilov and Bhattacharyya (Acta Mat. 2002).

This work aims to connect atomistic model with continuum theory of phase transformations in Shape memory alloys(SMA). A formulation of the Helmholtz free energy potential based on the Lennard-Jones potential has been developed. Lennard-Jones potential was used to describe the inter-atomic interactions in bi-atomic crystal of NiTi. The microscopic expressions of the instantaneous mechanical (continuum) variables of mass, momentum, internal energy and temperature have been derived in terms of the atomic variables. The developed Helmholtz thermodynamic potential is used in the context of the sharp phase front-based continuum framework proposed by Stoilov et. el.(Acta Mat. 2002) to study the micro-macro transition during the thermomechanical response of NiTi crystals. The developed model has been successfully used to predict the response of 1D single crystal system.

This paper deals with the micro-macro transition in shape memory alloy thin films using a recently developed sharp phase front-based 3D constitutive model outlined by Stoilov (2002), and originally proposed in the 1D context by Stoilov and Bhattacharyya (2002). The key ingredient in the model is the recognition of austenite and/or martensite variants as separate phases in a SMA domain. Evolution of the interface between these phases is taken as an indicator of a phase transformation in progress. A generalized Clausius-Clapeyron (CC) equation is derived from the continuity of chemical potential at the interface. The implications of the CC equation on the initiation of phase transforamtion are studied for various mechanical loading modes. Finally, the issue of micro-macro transition is examined in the context of stress-strain-temperature response of a CuAlNi SMA thin film.

The issue of phase transformations in shape memory alloys is revisited in the 1D context. We focus on problems where there is a sharp interface between the two phase of austenite and martensite. Apart from the usual conservations equations, it is proposed that an extra equation be used to render the system of equations complete, when a first-order transition is considered. Seen within this context, the following two approaches can be derived as special cases: (i) Leo et al approach where the phase boundary temperature is taken to be linearly related to the stress, (ii) Abeyaratne and Knowles approach where a kinetic relation is assumed. Certain other implications of the new approach are discussed in light of these special cases.

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